Two possiblities to consider: moisture issues (not enough water, an undeveloped root system, windy conditions) or verticillium wilt fungus (part of the
plant is affected and the rest looks fine).
Since this is the first summer for the
tree, I would assume that it is a watering issue. The soil should be well drained and evenly moist (not wet, not dry, just moist).
You may have to check the soil around it regularly until it becomes established. Water the ground around the root ball since it may lack a good root system. Normally, it is best to water deep and not often. But this is the
plant's first year and it is summer so give it a little break from that rule.
Luis